In the oil and gas industry the storage tanks for crude and refined products play a key part in the supply chain of hydrocarbons. Knowing the exact volume of these storage units plays a critical role when transferring products to and/or from the tanks. As a result of variations in external and internal conditions (i.e. temperature) and aging and also as a result of the weight of the liquid product (i.e. hydrostatic pressure), the tank volume can vary by as much as +/−0.2%. Considering a 250,000 barrel storage tank, this variation would result in a volume of +/−500 barrels in volume change.
As a result of the high value of petroleum hydrocarbons, there is a mandatory requirement for calibration of storage tanks. Tanks used for custody transfer must be calibrated such that the transferred volume is very accurately known (e.g., Less than 0.1% error). The most commonly used techniques to perform this are; manual strapping (API MPMS 2.2A), optical techniques (Optical Reference Line Method ORLM-API Chapter 2.2B, Optical Triangulation Method (OTM)—API Chapter 2.2C, Electro-Optical Distance Ranging Method (EODR)—API Chapter 2.2D) and liquid calibrations (API Standard 2555). However, these measurements have been found to produce errors and are considered non-effective. In some cases, the foregoing testing techniques require tank downtime (e.g., emptying of the tank or otherwise halting the tank operation temporarily), which accumulates additional costs to the losses incurred. Moreover, many of the foregoing testing techniques are invasive in that they require accessing the internal volume of the tank and also can be destructive.
In the oil and gas industry, ultrasonic probes have been used to determine the health and structural integrity of pipelines and vessels at localized points. Known systems for measuring wall thickness using ultrasound are based on the concept of using the time-of-flight (TOF) for sound to travel between the outer and inner surfaces of the wall to determine distance traveled. In such implementations, the TOF analysis of the ultrasonic signals return journey through the metallic medium (i.e. pipe or vessel) is used to determine the thickness of the wall and, thus, degradation as a result of corrosion. Similarly, there has been work on sending acoustic waves along the length of pipes to determine if there are cracks or other anomalies that would cause unexpected reflections. However, such systems are reliant on known or assumed pipe dimensions and are not configured to determine the geometric profile of the pipe. Rather, the geometric measurement of the container is assumed or determined using the known alternative methods mentioned above.
In the case of tank inspection, the aforementioned methods require high levels of calibration and also require a couple of days' worth of work (e.g., including the erection and use of high scaffolding to deploy the measuring systems and conduct the measurements). Therefore, calibration/measurement of the tanks is done infrequently, leading to erroneous tank volumes and lost sales revenue.
The existing methods for tank calibration present significant drawbacks. For instance, using the current standards, it can take 1-2 days of work to perform the calibration. As a result, calibration of storage tanks is performed infrequently thus leading to inaccurate measurements of the actual volume stored within the tank or transferred to and from the tank, which can be costly. For example, a traditional timeframe between calibrations can be between five and fifteen years.
What is needed are systems and methods for calibrating the volume of storage tanks that addresses the limitations associated with the efficiency of performing calibration using existing systems. More specifically, what is needed are systems and methods for accurately performing tank calibration that can be deployed and operated in a relatively quick, low-cost, and non-invasive manner. What is also needed is a system that can be deployed quickly and on-demand and thus facilitates detection of changes in tank volume on a more frequent basis (e.g., on a daily basis or even per-fill basis).
It is with respect to these and other considerations that the disclosure made herein is presented.